Common computer graphics display hardware (typically a cathode ray tube or liquid crystal display monitor) generates an image from the three additive colors, red, green and blue (often referred to as "RGB" format). Digital video, in contrast, is commonly stored in luminance/chrominance format ("YUV" for example). Simultaneous display of RGB and YUV data on the same screen is a common application. It typically involves conversion of different source data formats to a common color space format (generally RGB for computer monitors).
It is known in the prior art to provide stand alone conversion specific hardware to a computer system to enable the conversion from one color space to another. Further, it is known to use stand alone converters having programmable parameters. Such applications, however, can increase system size and cost, and add to the complexity of the system board designs.
It is also known to use host resident software routines to convert between color spaces. Such routines are undesirable as they tie up valuable host resources.
U.S. Pat. No. 5,402,513 issued to John C. Schafer on Mar. 28, 1995, discloses a video window generator that includes a YUV-to-RGB conversion circuit. As shown in FIG. 6 of the patent, and described in column 8, the YUV-to-RGB circuit requires numerous multiply and divide circuits. Such circuits add to the complexity of the design and can occupy valuable space on an integrated circuit.
U.S. Pat. No. 5,381,180 issued to Michael Keith on Jan. 10, 1995, discloses an apparatus for generating color look-up table (CLUT) format video. As described in column 4 of the patent, video data is upsampled to a YUV888 format. The data is then truncated to YUV544 format, and this 13-bit form used as an index to a 8192 entry look-up table. Each entry in the look-up table corresponds to one of 256 values in an eight bit look-up table. A drawback of the Keith patent is that it requires a large look-up table and provides only a limited number of colors (256).
It is therefore desirable to provide a method and apparatus for accomplishing color space conversion that does not result in the above mentioned drawbacks.